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1.3 THE OBJECTIVES OF THE STUDY
Generally, the aim of this study is developing the experimental method of biogas production from cassava effluent in biodigester. The result of the study can give
contribution to motivate small and middle industries to convert cassava effluent to biogas. The specific objectives of this study can be defined as follows:
a. Study of biogas production from cassava starch effluent by adding microalgae as
nitrogen source and yeast as substrate activator. b.
Study of biogas production from cassava starch effluent with the treatment of gelled and ungelled feed.
c. Study of pH control during biogas production using buffer Na
2
CO
3
. d.
Study of feeding management in the semi-continuous process of biogas production.
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CHAPTER II THEORITICAL REVIEW
2.1 TAPIOCA AND EFFLUENT
Indonesia has 1,205,440 hectares planted area and 21,990,381 tons cassava productionyear BPS, 2009. Tapioca is one of product made from cassava. The flow
diagram process of tapioca production process can be seen in the figure 2.1.
Mulya nto, 2005
Figure 2.1 Flow Diagram Tapioca Production Process From this process it can be identified that there is liquid and solid tapioca waste in
the level of extraction. The tapioca effluent is potential raw material to convert to biogas Anunputtikul,
et al
, 2004. Cassava
Peel the cassava Wash the peeled cassava
Grind the washed cassava Extract the starched
Filter the extracted starch
Sedimentation Residue slurry
Effluent
Dry the wet tapioca Wet tapioca
Dried tapioca Cassava
Peel the cassava Wash the peeled cassava
Grind the washed cassava Extract the starched
Filter the extracted starch
Sedimentation Residue slurry
Effluent
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2.2 BIOGAS
Biogas originates from bacteria in the process of bio-degradation of organic material under anaerobic without O
2
conditions. The natural generation of biogas is an important part of the biogeochemical carbon cycle. Methanogens methane producing
bacteria are the last link in a chain of micro-organisms which degrade organic material and return the decomposition products to the environment. In this process biogas is
generated, a source of renewable energy Werner Kossmann,
et al
, 2008. Biogas consists mainly of methane and carbon dioxide, but also contains several
impurities. It has specific properties which are listed in Table 2.1. Biogas with methane content higher than 45 is flammable Dieter Deublein, 2008.
Table 2.1 General Features of Biogas Composition
55 - 70 Methane CH
4
30 - 45 Carbon Dioxide CO
2
Traces of Other Gases Energy content
Fuel equivalent Critical pressure
Critical temperature Normal density
Smell Molar Mass
6.0 – 6.5 kWhm
3
0.60 – 0.65 L oilm
3
biogas 75
– 89 bar − 82.5° C
1.2 kgm
3
Bad eggs the smell of desulfurized biogas is hardly noticeable 16.043 kgkmol
Dieter Deublein, 2008
2.3 BIOGAS PRODUCTION PROCESS